My SO has a 2007 RAV4. It has an oil change reminder (a nice feature), so
the oil is getting changed at or shortly after the 5000 mile mark. After
about 9 months and around 20K total miles on the car (5K on that oil), I
took a sample and sent it off for analysis. The report said the oil was in
good condition and was probably good for at least another 3K miles.
Unless you are doing something unusual (taxi service, package delivery,
extensive idling), there is no reason to go to an oil change interval less
than the recommended 5k miles.
15 years ago when I last had oil tested, it cost about $50 Canadian. Back
then, I had gotten into the habit of having both oil and tranny fluid tested
every 3 years--worrying about major repairs sneaking up.
The test cost $22.50. I was curious. I have sent off a sample for many
vehicles over the years to try and get an idea if there were possible
engine problems brewing. In the case of the RAV4, given all the
stories about sludge, I wanted to make sure that if the engine
developed sludge, it wasn't my fault. It was nice to see that the oil
was still in good condition after 5,000 miles, even though I was
changing it. I'll probably send off another sample when the vehicle
has been driven around 60,000 miles.
If you are only paying $5 for 5 quarts of oil, you must be getting the
minimal quality stuff. The cheapest 5W20 oil I can find is nearly $2 a
quart. Castrol GTX is $3 a quart and Mobil 1 is $5 a quart.
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